Categorisation of reactions and enumeration of bacteria in potato cultivars inoculated with the causal agent of bacterial ring rot

Variability in the responses of plants propagated from in vitro tissue cultures of 52 ware and industrial potato cultivars to different Clavibacter michiganensis subsp. sepedonicus inoculum size was tested during 2015–2017. Bacterial ring rot symptoms on plants and tubers xylem vessels were recorded for 8 weeks and the susceptibility index (SI) for individual cultivars was calculated. Based on foliage symptoms, potato cultivars were placed into three symptoms groups. The symptomless group had SIs ≤ 1, for the moderate symptom group SIs ranged from 1.01 to 2.99, and the severe symptom group had SIs ≥ 3.0. The pathogen concentrations in vascular vessels of all infected potato plants increased during the experiment regardless of the foliage symptom group.

Antimicrobial efficacy of some plant extracts on bacterial ring rot pathogen, clavibacter michiganensis ssp. sepedonicus

Control of plant bacterial diseases remains difficult due to the limited availability of efficient plant protection products with reduced negative effects either in the environment or with human and animal health. In order to reduce the usage of chemical pesticides alternative strategies for controlling plant pathogens and improve plant disease resistance are promoted. The aim of the study was to investigate the antibacterial activity of some natural compounds (plant extracts of Tamarix ramosissima, Rosmarinus officinalis, Chelidonium majus, Silybum marianum, Satureja hortensis essential oil and propolis) against bacterial ring rot pathogen, Clavibacter michiganensis ssp. sepedonicus (Cms). An agar diffusion method was used for the screening of the inhibitory effect of natural compounds on bacterial strains’ growth. Minimum inhibition concentrations (MICs) were determined by a twofold serial dilution method. The anti-pathogenic activity was investigated by the study of anti-biofilm activity of natural substances. The analyzed natural substances showed a good microbicidal activity and anti-biofilm activity. The results obtained from this study may contribute to the development of new bio-control agents as alternative strategies for prevention and control of ring rot pathogen.

Teknik Inokulasi Buatan Clavibacter michiganensis subsp. sepedonicus, Penyebab Penyakit Busuk Cincin Bakteri, pada Tanaman Kentang (Solanum tuberosum L.)

ABSTRACT Inoculation Techniques of Clavibacter michiganensis subsp. sepedonicus, the Cause of Bacterial Ring Rot Disease, on Potato (Solanum tuberosum L.). Clavibacter michiganensis subsp. sepedonicus, the cause of bacterial ring rot disease on potatoes, has been detected in potato fields in Pangalengan. To anticipate the spread of the pathogen, researches on the desease epidemiology are urgent to be carried out. Artificial inoculation techniques will be useful in the epidemiological studies. The objective of this reasearch was to evaluate some inoculation techniques, which are simple, cheap and fast in causing disease symptoms. The experiment was carried out at the laboratory and glasshouse of Balai Penelitian Tanaman Sayuran (Balitsa), Lembang. The experiment was arranged in the randomized block design with five treatments of inoculation technique and five replications. The treatments were (a) soaking wounded seed tubers in pathogen suspension, (b) soaking not wounded seed tubers in pathogen suspension, (c) pathogen suspension was injected into leaf axil, (d) pathogen suspension was injected into seed tubers, and (e) pathogen suspension was poured into the planting holes. The results showed that stabbing and soaking tubers in pathogen suspension caused the shortest incubation period (17 days after inoculation) and the highest disease incidence (60%). Keywords : Clavibacter michiganensis subsp. sepedonicus, Bacterial ring rot, Potatoes, Inoculation techniquesABSTRAKClavibacter michiganensis subsp. sepedonicus (Cms), penyebab penyakit busuk cincin bakteri pada tanaman kentang, telah terdeteksi keberadaannya pada pertanaman kentang di Pangalengan. Dalam upaya mencegah penyebaran penyakit busuk cincin bakteri di Indonesia, perlu adanya studi epidemiologi patogen tersebut. Pada penelitian epidemiologi akan diperlukan cara menginokulasi tanaman secara buatan. Tujuan dari penelitian ini adalah untuk mendapatkan teknik inokulasi buatan yang dapat menyebabkan periode inkubasi yang lebih singkat dan persentase kejadian penyakit busuk cincin bakteri paling tinggi pada tanaman kentang. Percobaan dilaksanakan di rumah kaca dan laboratorium penyakit Balai Penelitian Tanaman Sayuran (Balitsa), Lembang. Percobaan dirancang secara rancangan acak kelompok dengan lima perlakuan teknik inokulasi Cms dan lima ulangan, yaitu inokulasi dengan (a) merendam ubi benih yang telah dilukai dalam suspensi bakteri, (b) merendam ubi benih tanpa dilukai dalam suspensi bakteri, (c) suspensi bakteri ditusukkan pada ketiak daun tanaman kentang, (d) suspensi bakteri ditusukkan pada ubi benih, dan (e) suspensi bakteri disiramkan pada lubang tanam. Masing-masing ulangan terdiri dari lima tanaman. Hasil penelitian menunjukkan bahwa dari lima teknik inokulasi buatan yang dilakukan, inokulasi dengan melukai ubi benih dan merendamnya dalam suspensi patogen menghasilkanJurnal Agrikultura 2016, 27 (2): 66-71ISSN 0853-2885Teknik Inokulasi Buatan Clavibacter….67periode inkubasi tersingkat, yaitu 17 hari setelah inokulasi, dan persentase kejadian penyakit tertinggi yaitu sebesar 60%.Kata Kunci : Clavibacter michiganensis subsp. sepedonicus, Busuk cincin bakteri, Kentang, Inokulasi buatan

New Type of Antimicrobial Protein Produced by the Plant Pathogen Clavibacter michiganensis subsp. michiganensis

ABSTRACTIt has previously been shown that the tomato pathogenClavibacter michiganensissubsp.michiganensissecretes a 14-kDa protein,C. michiganensissubsp.michiganensisAMP-I (CmmAMP-I), that inhibits growth ofClavibacter michiganensissubsp.sepedonicus, the causal agent of bacterial ring rot of potato. Using sequences obtained from tryptic fragments, we have identified the gene encodingCmmAMP-I and we have recombinantly produced the protein with an N-terminal intein tag. The gene sequence showed thatCmmAMP-I contains a typical N-terminal signal peptide for Sec-dependent secretion. The recombinant protein was highly active, with 50% growth inhibition (IC50) of approximately 10 pmol, but was not toxic to potato leaves or tubers.CmmAMP-I does not resemble any known protein and thus represents a completely new type of bacteriocin. Due to its high antimicrobial activity and its very narrow inhibitory spectrum,CmmAMP-1 may be of interest in combating potato ring rot disease.